1. Field of the Invention
This invention relates to an improved process for thermally stabilizing photoresist images and is more particularly concerned with the thermal stabilization of photoresist images having high resolution geometries for use in microelectronic applications.
2. Description of the Prior Art
In the aforementioned commonly assigned prior applications Ser. No. 802,514 now U.S. Pat. No. 4,701,390; 823,942; and 879,385 now U.S. Pat. No. 4,762,768 there are described processes for thermally stabilizing photoresist images such as those employed in the fabrication of microelectronic circuitry on chips, wafers and the like particularly such images having high resolution geometries. In the '514 application the thermally stabilizing agents are inclusive of fluorocarbon surfactants, hydroxyl group containing polymers, chromium sulfate, trichloroacetic acid, chromotropic acid and salts of the latter acids. In the '942 and '385 applications the thermal stabilization is accomplished by applying a film of a high temperature resistant film forming polymer of which hydrolyzed collagens such as gelatin and non-gelling hydrolyzed gelatins are preferred examples.
The processes of these prior applications have been found to give satisfactory results when employed with photoresist layers having a thickness of about 1 micron or less. However, when the thickness of the photoresist layer exceeds about 1 micron, it has been found that the coating of the thermally stabilizing agent can cause distortion of the photoresist image to which it has been applied. Cracks, breaks and like flaws in the image can result and, in some cases, the image may lose adhesion to the substrate and show a tendency to peel off. Any and all of these phenomenon can impair or destroy the high resolution geometry required in the photoresist image without which the desired final microcircuitry cannot be successfully produced.
It has been found that photoresist images which have thicknesses substantially in excess of about 1 micron can be thermally stabilized by a modification of the processes described in the aforesaid prior applications.